Adding support for Visual C's __declspec(noreturn) function declarations to perl

Adding support for Visual C's __declspec(noreturn) function declarations to perl

This will reduce the machine code size on Visual C Perl, by removing C stack
clean up opcodes and possible jmp opcodes after croak() and similar
functions.  Perl's existing __attribute__noreturn__ macro (and therefore
GCC's __attribute__((noreturn)) ) is fundamentally incompatible with MS's
implementation for noreturn functions. win32.h already has _MSC_VER
aware code blocks, so adding more isn't a problem.